Detection of biomolecules or their interactions has applications in many biological and biochemical industries. For example, it has been widely used for medical diagnostic applications.
Known detection devices of biomolecules and their interactions include microchips or biochips with arrays of addressable test sites thereon. Such devices are powerful analytical tools because hundreds or thousands of unique test sites can be analyzed simultaneously, with high throughput. In a typical conventional microchip, target molecules can be captured and immobilized at different spots on the microchip for detection. Different test sites may be used to detect different target molecules or the same molecules in different samples. Various techniques may be used to detect the target molecules. For example, the target molecules may be detected optically or electrically. Further, biomolecules or biomolecular interactions may be detected by the enzyme immunoassay (EIA) or enzyme-linked immunosorbent assay (ELISA) techniques, with extremely high sensitivity and specificity.
However, conventional microchips suffer certain drawbacks. For example, in known devices the test sites are often immersed in liquid during detection and cross-interference between different test sites can occur due to diffusion of the molecules to be detected from one test site to another. Such cross-interference can lead to false or inaccurate detection results. The molecules to be detected can be either the target molecules or reaction products which are to be detected to indicate the presence of the target molecules.
A known approach to avoid cross-interference due to diffusion is to increase the distance between different test sites, to reduce the effect of diffusion. For example, Ying Ding et al. disclosed a device based on the EIA electrochemical technique (EIA-EC) in “Feasibility studies of simultaneous multianalyte amperometric immunoassay based on spatial resolution”, Journal of Pharmaceutical and Biomedical Analysis, (1999), vol. 19, p. 153, the contents of which are incorporated herein by reference. In this detection device, each test site has a working electrode and the distance between two adjacent electrodes is 2.5 mm. This spatial separation is found to be effective for avoiding cross-interference caused by diffusion when the detection measurement is completed within a certain time period after introducing the enzyme substrate. However, such an approach also has some drawbacks. One problem is that only a small number of test sites can be formed on a microchip device when the distance between adjacent electrodes is so large.
An alternative known approach of optical ELISA or EIA is to provide an array of isolated test wells in a chip to avoid cross-interference caused by diffusion. However, these well-based microchips have their own limitations. One problem is that well-density is limited, due to either manufacturing or operation requirements, so that it is difficult to form high-density test sites. Another problem is that a well-based microchip does not allow flow-through operation, thus making automated operation difficult. For example, automated sampling, washing, or dilution on such a chip may require expensive equipments such as robotic devices.
Thus, there remains a need of improved devices and methods for detection of molecules and molecular interactions.